Four individuals, each of whom exhibit complete sex reversal, and who have minor phenotypic malformations have been recently identified. In each case, cytogenetic studies revealed an XY chromosome complement in addition to a deletion of the distal short arm of chromosome 9 resulting from unbalanced chromosomal translocations. Preliminary data suggest that the shortest region of common deletion of chromosome 9 in these individuals involves approximately 0.5 to 1.0 Mb of DNA. It is hypothesized that the common region of deletion contains a gene(s) involved in sex determination and hence, the cascade of events leading to normal sex differentiation. We have flow sorted a human derivative chromosome 8 resulting from this translocation between chromosome 8 and 9; t(8;9) (p21.1.1;p24). The DNA obtained from the flow sort is being amplified by DOP-PCR, labeled and used to screen chromosome 9-specific YAC and cosmid libraries, and a P1 total genomic library to isolate clones specific to 9p24. The identification of a gene(s) will be of significance in the clinical diagnosis and management of XY females and will also provide insight into the genetics of sex determination.